This invention relates to nonionic detergent compositions that provide an improved soil shield effect and exhibit reduced tower smoking during the detergent manufacturing process. More specifically, the invention concerns the use of nonionic surfactants of the ethoxylated C.sub.12-18 fatty alcohol type having a narrow ethylene oxide distribution in combination with modified cellulose ethers for detergent compositions. 2. The Prior Art
Condensation adducts of ethylene oxide with fatty alcohols have long been recognized as effective surfactants in detergent compositions. These adducts, a form of nonionic surfactant, are widely used in commerce.
Fatty alcohol ethoxylates are conventionally produced by reacting fatty alcohols with ethylene oxide in the presence of a catalyst. These reactions yield mixtures of alcohol derivatives with varying ethoxylate content. Individual components are rarely separated. Thus, what is commonly termed "an alcohol ethoxylate" is in reality a mixture of alcohol derivatives having a wide range of ethylene oxide units, including short chain adducts, as well as a certain proportion of unreacted alcohol. Moreover, the conventional designation of the number of ethylene oxide units present per molecule of an alcohol ethoxylate is actually a designation of the average weighted molecular distribution. There are substantial proportions of alcohol ethoxylate molecules present which have a greater or less number of ethylene oxide units than the actual average value would indicate.
Unreacted alcohol and short chain adducts are more volatile than the longer chain materials. Consequently, there is a tendency for these lower molecular weight compounds to be stripped from the main product during high temperature spray drying in detergent manufacturing. These volatiles then condense in the exhaust plume, as cooling occurs. Opaque droplets which result from the cooling reduce light transmission and comprise the "blue smoke" phenomena. Environmental regulations restrict the emission of "blue smoke". To overcome the problem, production rates of spray drying must be slowed to curtail smoking. Production capacity is accordingly lowered and operating costs are increased.
A second problem has been noted. Traditional broad ethylene oxide distributed alcohol ethoxylates in combination with modified cellulose ethers impart poor soil shield onto polyester and cotton/polyester fabrics. Soil shield is the protective coating of cellulosic deposited onto synthetic fabric during a wash in a detergent containing both a nonionic surfactant and a cellulose ether. Removal of oil and grease stains is facilitated in subsequent washes where fabrics have been soil shield treated.
A number of patents disclose efforts to improve the detergent activity and physical properties of alcohol ethoxylates by chemical modification. In U.S. Pat. No. 3,682,849, it was found that ethoxylate adducts derived from C.sub.11-15 alcohols having 80% straight-chain structures and 20% 2-alkyl branched-chain structures, when stripped of unreacted alcohol and lower ethoxylates, exhibited lower pour points, lower melting points, higher cloud points, lower gel temperatures and better detergency than previous ethoxylates. Mixtures of compounds having different degrees of ethoxylation (where one alcohol is ethoxylated with 8 to 20 ethylene oxide units and a second contains 2 to 6 ethylene oxide units) were described in U.S. Pat. No. 4,083,793 as improved nonionic textile washing compositions. End capping of ethoxylated alcohols has been another chemical method of achieving improved properties. For example, U.S. Pat. No. 4,098,713 terminates an ethoxylated alcohol with a glycerine cap. Carboxyalkylation has been another popular method of capping alcohol ethoxylates. References to carboxyalkylation can be found in U.S. Pat. No. 4,223,163 assigned to Procter & Gamble. The P&G patent also outlines a process for making ethoxylated fatty alcohols with narrow polyethoxy chain distribution. Less than 5 moles of ethylene oxide per fatty alcohol are employed in the P&G carboxyalkylated ethoxylate.
While the aforementioned improvements in alcohol ethoxylates have benefited detergency and other physical properties of detergent compositions, none has successfully addressed the problem of poor soil shield toward polyester and cotton/polyester blend fabrics. The tower smoking problem has also not been solved.